446 American Seashells 



Up to I % inches in length, moderately fragile, moderately elongate and 

 with the beaks central. Characterized by pecuhar, concentric undulations on 

 the beaks. This small species of Mactra is common in lagoons and bays of 

 southern California. It lives 3 to 6 inches below the surface of the sand. 



Mactra nasuta Gould Gould's Pacific Mactra 



San Pedro, California, to Mazatlan, Mexico. 



Up to 3/4 inches in length, similar to calif ornica, but more oval at the 

 ventral margin, without concentric undulations on the beaks, and with 2 very 

 distinct, raised, radial ridges on the posterior dorsal margin. The whitish 

 shell is glossy and the periostracum is shiny and yellowish tan. Not very 

 common. 



Genus Spisula Gray 1837 



Spisiila soUdissima Dillwyn Atlantic Surf Clam 



Plate 32P 

 Nova Scotia to South Carolina. 



Up to 7 inches in length (usually about 4 or 5 inches), strong, oval and 

 smoothish, except for small, irregular growth lines. The lateral teeth bear 

 very tiny, saw-tooth ridges. Color yellowish white with a thin yellowish 

 brown periostracum. Common below low-water mark on ocean beaches. 

 After violent winter storms, these clams are cast ashore in incredible num- 

 bers, some estimates giving an approximate count of 50 million clams along 

 a ten-mile stretch. 



The subspecies shnilis Say (Cape Cod to both sides of Florida and to 

 Texas) is more elongate, its anterior slope flatter, and its pallial sinus longer 

 and not sloping slightly upward. In the left valve, the tiny double tooth, 

 just anterior to the spoon-shaped chondrophore, is usually much larger and 

 stronger. Moderately common, and commonly existing with the typical spe- 

 cies in the northern part of its range. Compare with polynyma which has a 

 larger pallial sinus. 



Spisula polynyma Stimpson Stimpson's Surf Clam 



Plate 31W; figure 26k 



Arctic Seas to Rhode Island. Arctic Seas to Puget Sound. Also Japan. 

 3 to 5 inches in length, beaks very near the middle of the valve. Anterior 



